Trigemino-reticulo-facial and trigemino-reticulo-hypoglossal pathways in the rat

Abstract

This study was undertaken to identify premotor neurons in the pontomedullary reticular formation serving as relay neurons between the sensory trigeminal complex and the motor nuclei of the VIIth and XIIth nerves. Trigeminoreticular projections were first investigated after injections of anterogradely transported tracers (biotinylated dextran amine, biocytin) into single subdivisions of the sensory trigeminal complex. The results show that the trigeminoreticular projections were abundant from the pars interpolaris (5i) and caudalis (5c) and moderate from pars oralis (5o) of the spinal trigeminal nucleus. Injections into the 5i and 5c produce dense anterograde labeling (1) in the dorsal medullary reticular field; (2) in the parvocellular reticular field, medially adjacent to the 5i; and (3) more rostral in the region dorsal and lateral to the superior olivary nucleus. Some labeled terminals were also found in the intermediate reticular field, whereas only light anterograde labeling was observed in the gigantocellular and oral pontine reticular formation. The 5o sends fibers and terminals throughout the whole reticular formation, with no clear preferential projections within a particular field. Only light projections originated from the principal nucleus (5P). In a second series of experiments, we examined whether premotor neurons in the reticular formation are afferented by trigeminal fibers. Double labeling was performed by injection of an anterograde tracer in the 5i and 5c and retrograde tracer (gold-horseradish peroxidase complex) into the VII or the XII motor nucleus on the same side. Retrogradely labeled neurons in contact with anterogradely labeled boutons were found throughout the reticular formation with predominance in the parvocellular and intermediate reticular fields. These experiments demonstrate the existence of trigeminal disynaptic influences, via reticular neurons of the pontomedullary reticular formation, in the control of orofacial motor behaviors.

Experiential Modification of the Trigeminal Reflex Blink Circuit

“…Second, single-unit recordings of second-order corneal responsive neurons in the blink circuit show that there is no decrease in the response to a second corneal stimulus, although the blink evoked by the second cornea stimulus is significantly smaller (Henriquez and Evinger, 2007). Thus, suppression of the blink evoked by the second of two identical stimuli must not occur in the second-order trigeminal neurons, but probably occurs within the reticular part of the blink circuit Zerari-Mailly et al, 2001.…”

Activation of NPY receptors suppresses excitatory synaptic transmission in a taste-feeding network in the lower brain stem

“…input from brain stem orosensory and viscerosensory nuclei, including the rostral (gustatory) nucleus of the solitary tract (rNST), caudal (visceral) NST (cNST), the parabrachial nucleus, and ventrolateral medulla (8,28,31,54,64). Results from decerebrate preparations in which visceral signals, such as gastric load (49) and glucoprivation (15,21), modify the amount of a palatable (sweet) stimulus that is consumed, suggest that these local pathways exert a potent influence over this consummatory circuitry (reviewed in Refs.…”

Comparative Histological Study of the Mammalian Facial Nucleus

“…The ventral part of the Japanese monkey and dolphin (both Risso's and bottlenose species) facial nuclei differed in the columnar arrangement from the other examined mammalian species. The ventromedial and ventrolateral subnuclei correspond to regions shown to communicate with cells of the motor trigeminal and hypoglossal nuclei via premotor interneurons within the reticular nuclei [14,19,22]; therefore, species differences may arise from the developmental strategy behind the evolution of mastication.…”